Light Detection and Ranging (LiDAR) systems, also known as Laser Detection and Ranging (LaDAR) systems, in simplistic form, bounce a beam of light off a distant object and measure the precise amount of time it takes for that beam to return to the sensor.
Bouncing a light beam off of an object allows a LiDAR system to determine the distance to the object based on the speed of light and the time taken by the light to travel the distance to the object and back. In other words, LiDAR systems can be used for calculating how far the light traveled during the very short span of time from when the light beam's pulse left the laser in the system to when the light beam returned to a sensor in the system.
LiDAR systems typically include a deflection element that deflects the light beam in a specified direction before the light beam leaves the system. There are currently a number of methods to deflect the light beam with the deflection element such that the light beam sweeps or scans a path along the ground. One such method of producing this sweep is to use a rotating mirror as the deflection element.
Currently, the rotating mirrors used as deflection elements are typically an element having a cross-section in the form of a regular polygon shape in which all of the sides are the same length, such as a triangle, square, pentagon, hexagon, or other regular polygon shape. These shapes are also known as “extruded polygons” or regular polyhedrons, and can be described as a three-dimensional shape whose faces are regular polygons. The shape of a regular polyhedron may be visualized as a two-dimensional regular polygon that has been lengthened, at ninety degrees from the two-dimensional plane, so that the sides of the regular polygon have a height, forming a three-dimensional shape.
An exemplary conventional deflection element with a regular polyhedron shape is illustrated in FIG. 1a and FIG. 1b. In FIG. 1a and FIG. 1b, the deflection element has four sides A, B, C, and D. The sides of the conventional deflection element are positioned parallel to a central axis, also referred to as an optical axis, about which the conventional deflection element rotates.
As the light beam hits the surface of one of the sides of the deflection element, a reflective surface, such as a mirror, on the deflection element redirects the light beam along a path. In an aerial LiDAR system, for example one mounted on a satellite or aircraft, the path is typically perpendicular to the direction of travel of the aircraft and is typically aimed directly beneath (nadir to) the capture platform of the aircraft.
However, in some applications, it is desirable to not only acquire a directly nadir scan, but it is also desirable to capture an obliquely aimed scan, adapted to scan the vertical surfaces of buildings, structures, or other vertical objects in the path of travel.